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Reef Fish Added to List of Species With an Internal Compass

Baby reef fish are the latest in a long line of species shown to possess an internal magnetic sense.

Scientists have known for years that animals as diverse as birds, butterflies, marine mammals, and worms have a built-in sense of direction. Thanks to first-of-its-kind research, we can now add a tiny reef fish to the growing list of animals and birds that sense and respond to Earth’s magnetic field.

Professor Mike Kingsford, from the ARC Centre of Excellence for Coral Reef Studies at James Cook University, recently reported on his work with tiny Cardinal fish from One Tree Island on the Great Barrier Reef. Kingsford and his colleagues tested the fish’s orientation in total darkness using the same magnetic field as the Reef.

In a press release, Professor Kingsford explained that "Normally, fish orientated to the southeast, but when we altered the magnetic field clockwise by 120 degrees, there was a significant change in the direction the fish swam. They all turned further west, thinking they were still on track to their destination."

Scientists long held two rival theories about how magnetoreception works. One theory suggested that magnetic perception came from an iron-binding molecule which somehow triggered neural pathways to open or close. An alternate, biochemical sensor theory, suggested that magnetic fields trigger chemical reactions in proteins called cryptochromes, which have previously been associated with magnetic sense in birds.

However, a study published in 2015 suggested that the two mechanisms were part of the same system, and described in some detail how they fit together.

A team at Peking University in China screened the fruit fly genome for a protein with very specific characteristics: it had to bind iron; had to be expressed inside a cell, inside the animal’s head; and it had to interact with cryptochrome.

The researchers found one protein which fit their predictions and named it magnetoreceptor protein (MagR). According to New Scientist, when the team tested the MagR complexes in the lab, “the proteins snapped into alignment in response to a magnetic field.”

While the protein complex appears to form the basis of magnetoreception in some animals, the exact mechanism by which it operates is still unclear. The Chinese team lead, Can Xie, told New Scientist that one possible mechanism could be that when an animal changes direction, the proteins may swing around to point north like a compass needle. Alternatively, perhaps the proteins’ movement could trigger a connected molecule, which would send a signal to the nervous system.

Regardless of how it works, it is clear that the idea of a magnetic sense is no longer controversial: Baby reef fish and numerous other animals take advantage of the sense to move and migrate. It has already even been suggested that manipulation of magnetic fields could deter pests from invading crops: What a fascinating concept.